A variety of optical communications modules are used in optical networks for transmitting and receiving optical data signals over the networks. An optical communications module may be an optical receiver module that has optical receiving capability, but not optical transmitting capability. Alternatively, an optical communications module may be an optical transmitter module that has optical transmitting capability, but not optical receiving capability. Alternatively, an optical communications module may be an optical transceiver module that has both optical transmitting and optical receiving capability.
A typical optical transmitter or transceiver module has a transmitter optical subassembly (TOSA) that includes a laser driver circuit, at least one laser diode and various other electrical components. The laser driver circuit outputs an electrical drive signal to each respective laser diode to cause the respective laser diode to be modulated. When the laser diode is modulated, it outputs optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system of the module focuses the optical signals produced by each respective laser diode into the end of a respective transmit optical fiber held within an optical connector module that connects to the optical transmitter or transceiver module.
A typical optical receiver or transceiver module has a receiver optical subassembly (ROSA) that includes at least one receive photodiode and various other electrical components. An optics system of the ROSA focuses an optical data signal that is output from the end of an optical fiber onto a photodiode of the ROSA. The photodiode converts the incoming optical data signal into an electrical analog signal. An electrical detection circuit, such as a transimpedance amplifier (TIA), receives the electrical signal produced by the photodiode and outputs a corresponding amplified electrical signal, which is processed by other circuitry of the ROSA to recover the data.
Many different types of optical communications modules are available in the market, including single-channel optical transmitter and receiver modules, dual-channel optical transceiver modules, and parallel optical transmitter, receiver and transceiver modules. One type of single-channel optical transmitter module has a tube-shaped plastic optical port that is sized and shaped to receive a ceramic ferrule of an optical connector module. A proximal end of the plastic optical port merges into a plastic module housing of the single-channel optical transmitter module. The distal end of the plastic optical port extends outwardly from the plastic module housing. The interior of the plastic module housing houses the electrical components and the light source of the transmitter module.
In order to prevent back reflection of light produced by the light source of this type of single-channel optical transmitter module, a fiber stub disposed inside of the plastic optical port has a proximal end that is secured to the light source or to a lens of the module by a refractive index matching (RIM) epoxy. The distal end of the fiber stub is centered in the plastic optical port such that when the ferrule of the optical connector module is mated with the plastic optical port, a distal end of the ferrule is in a mated arrangement with the distal end of the fiber stub. In this mated arrangement, a distal end of an optical fiber held within the ferrule is in precise alignment with the distal end of the fiber stub such that the cores of the optical fiber of the ferrule and of the fiber stub are in precise alignment with one another.
The mating of the distal end of the fiber stub with the distal end of the ferrule is very important. The mated arrangement should provide precise alignment of the fiber stub and the ferrule to ensure that all or nearly all of the light produced by the light source is coupled from the fiber stub into the ferrule. In order to maintain such precise alignment, there should be no relative movement between the fiber stub and the ferrule. Relative movement between the fiber stub and the ferrule can only be prevented by ensuring that the outer diameter of the ferrule is exactly equal to the inner diameter of the tube-shaped plastic optical port such that there is no air gap between the outer diameter of the ferrule and the inner diameter of the tube-shaped plastic optical port. Due to manufacturing tolerances, however, these plastic parts cannot be made with such precision. For that reason, there is almost always an air gap between the outer diameter of the ferrule and the inner diameter of the tube-shaped plastic optical port that allows relative movement between the ferrule and the port to occur.
Furthermore, due to these manufacturing tolerances, it is possible that a worst-case scenario will occur in which the outer diameter of the ferrule is at a minimum value and the inner diameter of the tube-shaped plastic optical port is at a maximum value. In such a worst-case scenario, a very large air gap will exist in between the outer surface of the ferrule and the inner surface of the tube-shaped plastic optical port, which can result in a large amount of relative movement between the ferrule and the port.
Because it is not currently possible to eliminate these manufacturing tolerances altogether, a need exists for a way to prevent or at least reduce relative movement between the optical port and the ferrule.